The present invention relates to a method for synchronizing the motion sequences of at least one main pile and at least one auxiliary pile in a feeder or delivery device of a printing material processing machine having a drive for moving the main pile and a main pile controller associated with the drive, as well as an additional drive for moving the auxiliary pile including an auxiliary pile controller associated with the additional drive.
In sheet-fed rotary printing presses, the printing materials are fed from a feeder pile, which has to be regularly replenished when depleted. To this end, the feeder is essentially composed of a lifting device carrying a pallet with sheet stock. In the known feeders, a suction device removes sheet after sheet from this pile of sheet stock. In order that the sheet located on top of the pile is always at the same level, it is necessary to lift the pallet along with the sheet stock in the direction of the suction device, since the pile of sheet stock shrinks further and further due to the removal of sheets at the top. To prevent stoppage of the printing press when the pallet is depleted, many sheet-fed printing presses now have so-called “non-stop feeders”, which make it possible to load a new pile of sheet stock before the old pile is completely depleted. This means that the new pile must already be loaded while sheets are still removed from the rest of the old pile. To this end, the non-stop feeder has a pile-changing device, such as a movable rake, which is slid under the depleting pile. In this manner, the pile is lifted from its pallet so that the pallet can be lowered by the lifting device of the main pile, removed, and a new pile is placed in the feeder along with the pallet. In the next step, the new pile must now be merged with the small remaining pile, that is, the main pile approaches the remaining pile until it touches the remaining pile. After that, the rake must be removed from below the remaining pile, which takes a certain time.
During this time, however, the new main pile and the remaining pile that is left over must carry out the same sequences of movements to prevent the main and auxiliary piles from diverging apart. This requires precise control of the drive motors of the main pile and auxiliary pile devices.
German Patent DE 197 35 895 C1, related to U.S. Pat. No. 6,142,463 which is hereby incorporated by reference herein, describes several ways to move the auxiliary and main piles synchronously. One way is to control the drive of the auxiliary pile device so that it tracks the drive of the main pile device; the movement of the main pile being monitored by sensors, thus making it possible to generate appropriate control commands to control the auxiliary pile. Another possibility described in German Patent DE 197 35 895 C1 is to control the drives of the main and auxiliary drives with on-times of equal duration, the intention of which is to produce lifting movements of equal length of the main and auxiliary piles. These methods have the disadvantage that the drives do not move synchronously in time, but only travel the same path. This means that one of the piles begins to move later than the other one. However, this results either in gaps between the main and auxiliary piles, or in slight collisions between the main and auxiliary piles. Moreover, on-times of equal duration will produce calculable travel paths only in the case of constant external conditions. As soon as a parameter, such as the pile weight, changes, the travel path changes too, thus making it completely impossible for the main and auxiliary piles to move synchronously.